1. Field of the Invention
The present invention relates in general to valves for mineral recovery wells, and in particular to actuators to actuate valves.
2. Brief Description of Related Art
A gate valve is a valve having a body and a bore through the body. A gate is positioned transverse to the body, and moves linearly to obstruct flow through the bore or allow flow through the bore. Some gates have an aperture that aligns with the bore to allow flow. The gate can be normally open, and thus the gate is closed when it is moved linearly to push the aperture out of alignment with the bore. Alternatively, a gate can be normally closed, and thus the gate is opened when it is moved linearly to position the aperture in alignment with the bore. Regardless of whether the gate is normally open or normally closed, the gate is moved, or actuated, by a valve actuator.
Actuators can be a hydraulic, piston type actuator, or actuators can be a pneumatic piston or diaphragm type actuator. In conventional diaphragm actuators, a diaphragm is moved in response to pressure media, such as gas or other fluids, urging the diaphragm toward the gate valve. The diaphragm is partially supported by a support plate. When the diaphragm is urged downward, it urges the support plate downward, which then transfers the downward force via a stem to the gate of the gate valve. The outer diameter (“OD”) of the diaphragm support plate does not extend to the inner diameter (“ID”) of the housing in which the diaphragm is positioned, so a portion of the diaphragm hangs over the edge of the support plate and is thus unsupported. As one of skill in the art will appreciate, unsupported regions of a diaphragm are more prone to failure and require a thick and reinforced diaphragm to be able to withstand the force exerted by the pressure media.